Find the radius and centre of the circle given x^2+4x+y^2+2y=20
Complete the square:x2+4x gives (x+2)2-4y2+2y gives (y+1)2 -1Therefore,(x+2)2-4+(y+1)2 -1=20Rearranging gives:(x+2)2+(y+1)2 =25Comparing to the standard equation for a circle:(x-a)2+(y-b)2 =r2Means the radius = 5 (sqrt(25)) and the centre of the circle is (-2,-1)
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